Adjustable slot antenna



Nov. l1s., 1960 w. SERNIUK ADJUSTABLE `sLoT ANTENNA' 3 "sheets-S I8 heetA 1 mK Nw mm mEy S R E m W O/ZM/QLJ ATTORNEY W. SERNIUK ADJUSTABLE SLOT 4A IITEININTA Nov. 1v5, 1960 3 Sheets-Sheet 3 Filed Feb. 10. l1956 INVENTOR. WALTER SERNIUK ATTORNEY United States Patent() ADJUSTABLE SLOT ANTENNA Walter .Serniulo Palo Alto, Calif., assignor, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware IFiled Feb. 10, 1956, Ser. No. 564,675

14 Claims. (Cl. 343-768) This 'invention `pertains `to `tunable antennas, and more kparticularly to a mechanically driven tunable slot antenna adapted to be cyclically swept over a band of frequencies.

Prior known slot antennas have a natural frequency, determined by the fixed geometry of the slot. While slot antennas resonate in several modes of resonance, their natural frequency lis not continuously variable. For example, a slot antenna whose slot is closed at both ends resonates as a half wave resonator, a full wave resonator, a one and half wave resonator, etc. As another example, an open ended slot antenna resonates as a quarter wave resonator, a three quarter -wave resonator, a ive quarter wave resonator, etc. vWhen a slot with closed ends is utilized as a frequency determining element, it resonates as a half wave resonator. When an open ended slot is used as a frequency determining element it resonates as a quarter wave resonator. A circuit wherein the slot antenna is utilized as both a frequency determining member and a radiating member is shown in Patent Number 2,555,443, issued in the name of N. L. Harvey for Radio Apparatus Employing Slot Antenna. When the slot antenna is utilized as a frequency determining member in a transmitter, the oscillation generator is preferably connected to the slot at a high impedance point, i.e. at `the center of 1a half wave slot, or at the open end of a quarter wave slot, while in a receiver the detector is directly coupled to the slot in the same way;

An illustrative embodiment of the present invention is adapted to continuously vary the electrical length of a lslot antenna vby continuously varying the geometry of the slot antenna. In a preferred embodiment o'f `this vinven-v tion (the length of the lslot antenna is continuously 'varied without 4discontinuities from its maximum `=length to Vits minimum length, or alternatively from its minimum length to its maximum length. In such Ian embodiment the natural frequency of the slot antenna varies contnu- 'ously from a low value to a high value, or from a `high value to a low value. When such a slot antenna is connected to `a detector so that it constitutes the frequency determining element of the receiver, the tuned `frequency of the receiver is continuously swept and maybe utilized, for example, to detect incoming radio signals of unknown frequency appearing anywhere within a wide spectrum of frequency. When the antenna of this invention is connected as a frequency determining member for 'the radiated energy from Ya transmitter, the frequency of ythe radiated energy is continuously swept so that the transmitter can be used, for example, with a wide band frequency sweep, for radio jamming.

A pair of the antennas of this inventiomone connected to a transmitter, and one connected to a receiver, can 'be used when the antennas of the pair are synchronized, to communicate between the two antennas without interception. By varying the contour of the shutters, `described more particularly hereinafter, the resonant or natural frequency of the `slot antenna can be varied as a predetermined function of the motion of a drive mechanism, for example, the motion of a motor drivenshaft.

Patented N ov. 1 5, n 1 960 It is an object of this invention to simplify the structure of swept frequency transmitters and receivers.

It `is another object of `this `invention to sweep tune ya tunable slot antenna by continuously varying the effective electrical length of said slot antenna.

lIt -is a more particular obiect of this `invention to pro- -vide in connection with a tunable slot antenna novel means for periodically varying the electrical length of said slot antenna.

' It is still another object of this invention to provide means forming .a tunable slot antenna in a conducting vsheet member, in combination with mechanically driven tuning means adapted to periodically vary the electrical length of saidslot antenna.

It is still another robject of this invention to provide means forming a tunable slot antenna in combination with mechanically driven "tuning means adapted to symmetrically and periodically vary the electrical length of said slot antenna. 'i

Other objects will :become apparent from the following complete description ttaken in -connection with the accompanying drawings in which:

Figure l is a side view of `one embodiment of this invention;

Figure 2 is a view, partially in section, of the embodi ment of Figure `l;

Figure 3 is a vview taken at '3-3 in Figure 2;

Figure 4 is a view of a second embodiment of this invention;

Figure 5 is a view, partially in section, taken at 5-5 'in Figure 4;

Figure v6 is a view, partially in section, taken at 6-6 v'in Figure -4;

Figure '7 is a third embodiment of the device of this invention;

Figure 8 is a view taken at 8 8 in Figure 7.

The antenna shown in Figures 1, 2 and 3 include a Icylindrical conducting `sheet member 11 kwhich may be mounted, for example, in the air on the end of a pole. Means forming a slot 12 is cut or otherwise formed in lthe side of sheet member 11 with its long dimension parallel tto the axis thereof. Shaft 14, preferably fabrifcated of nonconducting material, is rotatably mounted 4within lcylinder 11 upon bearings at each end of cylinder 111. The bearings 16 are preferably fabricated `of as many nonconducting parts as possible. A pair of conducting tuning shutters 20 and 22, shown more clearly in the apar-tial ysection view `of Figure 2, are mounted concen- .trically upon -zshaft 14 to be rotated thereby. Shutter 20 is mounted upon shaft 14 by means of web 30, shown more rparticularly in Figure 3, so that it may rotate withfin cylinder 11 as close to the inner wall as possible but -not in `contact therewith. Shutter 22 is similarly mounted '-upon shaft `14 by means of a web (not shown) `similar .to web 30. Shutters 20 and 22 are fabricated of confducting .material and are positioned to intercept equal portions of slot 12 at `all angles of rotation. It is to be noted that slot "12 is closed at both ends and is a half 4vwavein length at the lowest operating frequency of the band over which the 'antenna is designed to be operated. In va half wave slot the high impedance point is at the center at point 13. Transmitters and receivers associated with such antennas are customarily attached to this high impedance point. Now in order to avoid the necessity of moving the connections of the transducer element, be -it oscillator, generator, or detector, as the frequency is fswept, it is preferable to symmetrically shorten or length- Ien :slot T2 about its mid-point. The portions of slot 12 "interceptedlby shutters 20 and 22 are symmetrical about the .mid-point 13 of slot v12. The clearance provided between shutters 2.0 and 22 and cylinder 11, as shown at A24 and26, 4,provide a .capacitive short across the slot at the points of intersection between slot 12 and the edges of shutters 20 and 22. Clearances 24 and 26 reduce the frictional dissipation of the power of motor 28 when shutters 20 and 22 are turned and' avoid noise due to intermittent contact. Clearances 24 and 26 are preferably as small as possible without mechanical interference .between shutters 20, 22 and cylinder 11.

Shaft 14 is connected to be driven by motor 28.' It is .to be noted that shaft 14 is not necessarily concentric with cylindrical sheet 11. It is only necessary that shaft 14 be positioned so that shutters 20 and 22 properly tune slot 12. Motor 28 can turn either clockwise or counterclockwise. The adjacent edges of shutters 20 and 22`are -so contained that, in operation, the electrical length of slot 12 is varied as a linear function, or any other predetermined desired function, of the angular rotation -of shaft 14. It is sometimes typical to shape shutters 20 and 22 so that the natural frequency of slot antenna 12 is varied smoothly from a low value to a high value, then is smoothly varied from the high value back to the low value. Alternatively, the natural frequency of the slot may be smoothly and gradually swept in one direction and abruptly in the other as would be done with the shutters shown in Figures l, 2 and 3.

A second embodiment of the present invention is shown in Figures 4, and 6, wherein the radiating slot 34 is provided in conducting sheet 32. At each end of slot 34 is a rotatable conducting shutter 36 and 38. Shutters 36 and 38 are identical and are positioned to intercept equal portions of slot 34, symmetrically about the mid-point 33 of slot 34. Shutters 36 and 38 are positioned substantially parallel to the plane of slot 34. Shutters 36 and 38 are mounted upon shafts 40 and 42 which are supported for rotation about axes perpendicular to the plane of slot 34. Shafts 40 and 42 are connected to be driven in opposite directions by any conventional means such as motor 44 and a closed belt system, shown more particularly in Figures 5 and 6. Motor 44 drives shaft 42 and pulley 50. Pulley 50 is connected to drive belt 46 which, in turn, is connected to drive pulley 48 and shaft 40 in a. direction opposite to the direction of rotation of shaft 42. When the shutter contour of shutters 36 and 38 is as shown in Figure 4, the natural frequency of slot antenna 34 is varied as a linear function of the rotation of shafts 40 and 42. By altering the contour of shutters 36 and 38, the natural frequency of slot 34 can be varied as any predetermined function of the rotation of shafts 40 and 42, for example, from a low to a high value then back to a low value without discontinuities.

In Figures 7 and 8, conducting sheet 52 contains means forming a slot 54. Conducting belt 56 is wrapped around driving rollers 58 and idler 64. Idlers 60 and 62 are positioned to align belt 56 parallel to sheet 52. Rollers 58, 60, 62 and 64 are positioned in suitable bearings 65 so that belt 56 travels along the length of slot 54. Conducting belt 56 forms an endless band of a conducting material as shown more particularly in Figure 9. It is provided with a pair of opposed slots 68 and 70 so that they coincide when they are directly over slot 54. Slots 68, 70, and S4 are preferably, although not necessarily, identical in shape and size. It is preferable that slots 68 and 70 be identical so that the shuttering effect of slots 68 and 70 is symmetrical about the mid-point of slot 54. When the belt 56 is moved, slot 68 moves in a direction opposite to the direction of motion of slot 70. Slot 68 acts as a shutter to close one end of slot 54, while slot 70 acts as a shutter to close the other end of slot 54. When slots 68 and 70 start to come into coincidence, the exposed portion of slot 54 is uniformly opened until slots 68, 70, and 54 come into complete coincidence. Further travel of belt 56 causes the exposed portion of slot S4 to decrease in length until the slot becomes completely closed.

In each of the embodiments above described the structure is symmetrical about the mid-point of a half wave slot which is the high impedance point to which the transducer means with which the antenna is to be operated is connected, while the low impedance points are swept to and from the center in order to turn the device. In circumstances where space is a factor and the radiation characteristics of a quarter wave slot are desired, or when either of these factors is so desirable as to overcome the disadvantages of the other, either half of the above antennas cut along the plane of symmetry lying normal to the length of the slot and through the feed point may be used.

In operation of the device of Figures 1, 2 and 3, motor 28 turns shaft 14 at preferably a uniform angular speed. Shaft 14 turns shutters 20 and 22 which mask off equal portions of slot 12 to vary the electrical length of slot 12. Assuming, for example, that motor 28 is turning in a clockwise direction, shutters 20 and 22 cause the electrical length of slot 12 to be varied from a maximum to a minimum then to change suddenly to a maximum and repeat the cycle. Thus the natural frequency of slot antenna 12 is varied from a predetermined low value to a predetermined high value and then suddenly jumps to said predetermined original low value.

In operation of the device of Figures 4, 5 and 6, shutters 36 and 38 turn in opposite directions about their respective shafts 40 and 42 to symmetrically vary the electrical length of slot antenna 34. Assuming that motor 44 turns shaft 42 in a counter-clockwise direction, as shown in Figure 4, shutter 36 is turned in a clockwise direction by means of belt 46 and pulleys 48 and 50. Shutters 36 and 38 intercept varying portions of slot 34 to vary the electrical length from a maximum predetermined value to a minimum predetermined value. The natural frequency of slot antenna 34 is varied from a predetermined low frequency to a predetermined higher frequency then, when shutters 36 and 38 unmask slot 34, suddenly shifts to said predetermined lower frequency.

In operation of the device of Figures 7 and 8, the natural frequency of slot 54 is varied from a predetermined high value to a predetermined low value, then is varied back to a predetermined high value. Motor 66 turns drive roller 58 which in turn drives belt 56 over roller 58 and idler 60, 62 and 64. At one point of the travel of belt 56, slots 68 and 70 are in the roller portion of their travel and slot 54 is completely masked closed. As belt 56 continues to travel, slot 68 starts to overlap or coincide with slot 70 and the length of the exposed portion of slot 54 continues to increase until slots 68 and 70 come into coincidence. Further travel of belt 56 causes the exposed length of slot 54 to decrease until slot 68 and 70 no longer coincide and slot 54 is completely closed.

It is to be understood that the physical length of the slot is not the same as the electrical length. For example, the physical length of the slot may be 0.6 wave length of the natural frequency wave, while the electrical length is a half wave length. The difference between the physical and electrical Wave length is caused by end effects, geometric effects, and capacitive effects.

All moving parts except the shuttering portion of all the embodiments of this invention are preferably of nonconducting material to avoid the introduction of noise and spurious frequency effects into the output of the antenna.

The device of this invention provides a novel tuning arrangement for mechanically tuning slot antennas to adapt the slot antennas to periodically sweep a band of natural frequencies. When a tuned slot antenna is connected by its high impedance point to a detector, it provides a simple receiver particularly adapted to sweep over the band of frequencies. Similarly. when the antenna of this 1'nvention is connected at its high impedance point to a grid and anode circuits of an electric discharge tube in a Hartley circuit a simple transmitter is provided which is particularly adapted to sweep the oscillation frequency of the transmitter over a band of frequencies.

Several embodiments of this invention have been shown but it is not intended to limit the device of this invention to the embodiments shown. The scope of the inveution is limited in accordance with the spirit thereof as set forth in the following claims:

What is claimed is:

1. A tunable slot antenna comprising a conducting sheet member; means forming a slot having closed ends in said sheet member; and mechanically driven tuning means symmetrcal about the mid-point of the length of said slot adapted to periodically vary the electrical length of said slot symmetrical about said mid-point.

2. A tunable slot antenna comprising a conducting sheet member; means forming a slot in said sheet member; first and second identical conducting shutters positioned respectvely adjacent the ends of said slot; means for periodically moving said shutters to intercept said slot symmetrically about the mid-point of the length of said slot; and motive means attached to said shutters to drive said shutters in synchronsm.

3. A tunable slot antenna comprising a conducting sheet member; means form'ng a slot in said sheet member; first and second conducting shutters over-lying said slot; second means forming a slot in said first conducting shutter; third means forming a slot in said second conducting shutter; at least said second and third slots being identical in shape; said second and third means formng a slot being adapted to be aligned with said rst slot; and means for moving said first and second shutters in opposite directions to symmetrically shorten the electrical length of said iirst slot.

4. A tunable slot antenna comprising a rst, second and third conducting sheet member; means forming a iirst, second and third identical slot in said lirst, second and third sheet members respectively, said second and third slot being adapted to be aligned with said rst slot; and mechanical means for moving said second and third conducting sheet members in opposite d'rections along the length of said i'rst slot to vary symmetrically the electrical length of said rst slot.

5. A tunable slot antenna comprising a rst, second and third planar conducting sheet member; means forming a first, second and third identical slot in said iirst, second and third sheet members respectively; said slots adapted to coincide in one position of said second and third members and mechanical means connected to said second and third sheet members to move said second and third slot in opposite directions along the length of said rst slot to symmetrically vary the electrical length of said iirst slot.

6. A tunable slot antenna comprising a conducting sheet member; means forming a slot in said sheet member; a rst rotatable conducting shutter positioned at one end of said slot; a second rotatable conducting shutter positioned at the second end of said slot; said shutters being identical and positioned to intercept equal portion of said slot; and mechanical means adapted to move said shutters in synchronism to intercept equal and varying portions of said slot to symmetrically vary the electrical length of said slot.

7. A tunable slot antenna comprising a planar conducting sheet member; means forming a slot in said sheet member; a rst conducting shutter rotatably mounted at a rst end of said slot to turn about an axis perpendicular to said sheet member; a second conducting shutter rotatably mounted at the second end of said slot to rotate about an axis perpendicular to said sheet member, said shutters being identical and adapted to intercept equal portions of said slot to symmetrically tune the electrical length of said slot; and means for symmetrically rotating said shutters.

8. A tunable slot antenna comprising a cylindrical conducting sheet member; means forming a slot in said sheet member; a pair of conducting tuning shutters positioned adjacent opposite ends of said slot, said shutters being identical and positioned to intercept equal portions of said slot; and mechanical drive means attached to said shutters to move said shutters to symmetrically Vary the electrical length of said slot.

9. A tunable slot antenna comprising a cylindrical conducting sheet member; means forming a closed slot in said sheet member; a pair of conducting tuning shutters positioned adjacent opposite ends of said slot adapted to rotate about an axis parallel with the axis of said cylindrical member, said shutters being identical and positioned to intercept equal portions on opposite ends of said slot; and mechanical drive means attached to said shutters to rotate said shutters about their axis of rotation to symmetrically vary the electrical length of said slot.

l0. A tunable slot antenna comprising a conducting sheet member having an elongated slot with closed ends formed therein, and driven tuning means arranged to vary the electrical length of said slot symmetrically about its mid-point.

l1. A tunable slot antenna comprising a conductive sheet member having an elongated slot with closed ends formed therein, land driven shutter means adjacent said slot arranged to vary the electrical length of said slot symmetrically about its midpoint.

12. A tunable slot antenna comprising a cylindrical conducting sheet member having an elongated slot with closed ends formed therein, a pair of cylindrical shutter members disposed within said cylindrical sheet member for rotation about an axis parallel to the axis of said cylindrical sheet member, said shutter members having contours such that upon rotation thereof the electrical length of said slot is varied symmetrically about the midpoint thereof.

13. A tunable slot antenna comprising a hollow circular cylindrical conductor having an elongated slot formed in the wall thereof parallel to the longitudinal axis of said conductor, and cylindrical shutter means rotatable within said conductor about an axis parallel to the longitudinal axis of said conductor arranged to vary the length of said slot symmetrically about its midpoint.

14. A tunable slot antenna comprising a conducting sheet member having an elongated slot formed therein, and a pair of planar conducting shutters mounted for rotation in a plane adjacent and parallel to said sheet member about points at opposite ends of said slot, respectively, said shutters having identical contours and arranged such that upon rotation thereof the electrical length of said slot is varied symmetrically about its midpoint.

References Cited in the le of this patent FOREIGN PATENTS 600,433 Great Britain Apr. 8, 1948 

